1. Field of the Invention
The present invention is generally related to functional magnetic resonance imaging and the hemodynamic response to cognitive stimuli and is more specifically related to diagnosing and measuring vascular drainage insufficiency in the central nervous system using fMRI and BOLD.
2. Related Art
When the brain is active, it requires an increase in blood flow to the brain cells in the active region. The increase in blood flow typically occurs after a brief delay (e.g., 1-5 seconds) and usually peaks at around 4-5 seconds. After the peak, the increased blood flow washes out and typically exhibits a negative trough before returning to a normal baseline level. This process of increased blood flow and corresponding washout is referred to as a hemodynamic response (“HDR”).
When the increased blood flow is delivered to the active region of the brain, the brain cells use the oxygen and glucose in the blood. Consequently, the deoxygenated blood remaining in the veins is paramagnetic and can be successfully imaged using magnetic resonance imaging. Imaging based on the magnetic contrast of deoxygenated blood is referred to as blood-oxygen-level dependence (“BOLD”).
Functional magnetic resonance imaging (“fMRI”) is used to capture complete scans of the brain during the HDR process, which typically takes about 15 seconds overall. The result of fMRI is a series of scans of the subject over time that show what region of the brain was active during the HDR. A single scan includes a full set of slices that cover the brain of the subject. Each slice is a separate image and collectively the slices comprise a three dimensional image of the brain of the subject. Typically, a scan is taken every 1-4 seconds. In this fashion, fMRI is used to identify the region of the brain that is active for a particular cognitive task.